1. Field of the Invention
The present invention relates to a controller and an LED driving circuit, and more particularly a controller and an LED driving circuit with protection function.
2. Description of Related Art
FIG. 1 is a circuit diagram of a conventional LED driving circuit. The LED driving circuit comprises a driving unit 110, an LED module 120, an N-type MOSFET 130, a current detecting resistance 140 and an error amplifier 160. The driving unit 110 is coupled to a terminal of the LED module 120 to provide a driving voltage VDR to drive the LED module 120 for lighting. The N-type MOSFET 130 is coupled to the other terminal of the LED module 120 to control an amount of a current flowing through the LED module 120 according to a control signal. The current detecting resistance 140 is coupled to the N-type MOSFET 130 to detect the amount of the current flowing through the LED module 120 and generate a current detecting signal Ifb. The error amplifier 160 receives the current detecting signal Ifb and a current set signal generated by a current set unit 150 and accordingly outputs a control signal to the N-type MOSFET 130 to control the amount of the current flowing through the N-type MOSFET 130.
A voltage in a drain of the N-type MOSFET 130 may be increased when one or more LEDs of the LED module 120 are short-circuited. Therefore, a power consumption of the N-type MOSFET 130 is also increased to cause a temperature increased thereof. Further, a safe operating area of the N-type MOSFET 130 is diminished when operating in a high temperature and so a reliability of the N-type MOSFET 130 is decreased or even the N-type MOSFET 130 is damaged.